With the technology development and the growing demands for a mobile device, an electric vehicle, a hybrid electric vehicle, an energy storage system, an uninterruptible power supply, and the like, the demand for a secondary battery as an energy source is dramatically increasing, and in this context, many studies are being conducted on batteries to meet various needs.
A secondary battery is a device that stores electrical energy in chemical form and converts the stored chemical energy into electrical energy to generate electricity when needed. The secondary battery is also referred to as a ‘rechargeable battery’ because it can be recharged repeatedly. A common secondary battery includes a lead accumulator, a NiCd battery, a NiMH accumulator, a Li-ion battery, a Li-ion polymer battery, and the like. When compared to a disposable primary battery, not only is the secondary battery more economically efficient, it is also more environmentally friendly.
Generally, most secondary batteries have a cylindrical, prismatic, or pouch shape. These secondary batteries are classified into pouch-type, cylindrical, and prismatic secondary batteries based on a type of an outer case. The secondary batteries have advantages of easy fabrication and low manufacturing costs because the secondary batteries are fabricated by mounting an electrode assembly composed of an anode, a cathode, and a separator in a cylindrical or prismatic metal can or a pouch-shaped case of an aluminum laminate sheet, and by injecting an electrolyte into the electrode assembly. When a predetermined mounting space for the secondary battery is required, there is a drawback in that adaptation in shape is limited. Thus, the cylindrical, prismatic or pouch shape of the secondary battery is a limitation in developing various shapes of mobile devices. Accordingly, there is a need for a new type of secondary battery that is easily adaptable in shape.
To fulfill this need, suggestions have been made to develop a cable-type secondary battery having a very high ratio of length to cross-sectional diameter. Korean Patent Application publication No. 2005-99903 discloses an adaptable battery consisting of an inner electrode, an outer electrode and an electrolyte layer interposed therebetween. Such secondary battery is mainly characterized by having a so-called cable structure which is constructed in an elongated shape and is flexible in a lengthwise direction.
Meanwhile, intensive studies have been conducted on an apparatus for charging a cable-type secondary battery that supplies power to the cable-type secondary battery.